When I received the book in the mail, I set it aside, thinking it would be a somewhat boring listing of things I already knew. When I finally got around to reading it, I was surprised and delighted. It held my interest, reminded me of things I had forgotten, explained other things I had never heard of, and provided entertaining stories to illustrate each point. Best of all, the bulk of his examples are taken from medicine and relate directly to the topics we discuss on SBM.

Carroll is well-qualified to write about logical fallacies: he is a retired professor of philosophy who has long promoted skepticism and taught classes in critical thinking, and he writes in an entertaining, accessible style. He started The Skeptic’s Dictionary website in 1994 with 50 articles and it has now grown to several hundred articles. It attracts more than a million visitors a month, and some of its entries have been translated into more than a dozen languages. It has become a go-to reference for anyone seeking the facts on questionable claims about everything from crop circles to homeopathy. Its articles are thorough and well documented with lots of references and links.

I am partly responsible for this book, as he explains in the acknowledgements and Preface. I reviewed his e-book Unnatural Acts: Critical Thinking, Skepticism, and Science Exposed! for Skeptical Inquirer in 2012. The original version of that book included a list of 59 fallacies, biases, and illusions that readers could learn about on their own. I suggested that he add a short description of each fallacy rather than simply listing their names, and he did. This led him to expand on the descriptive paragraphs in a blog, addressing one each week for 59 weeks. The new book is a re-organized and improved version of those blog posts.

He starts with a case study of an anti-vaccine activist, Stephanie Messenger, who wrote the unfortunate Melanie’s Marvelous Measles, a book that teaches unvaccinated children to welcome childhood diseases. He tells her story with insight and understanding. She had a child who became ill after vaccination and eventually died. She was desperate to understand why and to have the power to protect her other children from a similar fate. The specialists caring for her child suspected Alexander disease, a rare genetic neurodegenerative disease, but for some reason she rejected that possibility and became convinced that vaccines were responsible. Carroll details the series of fallacies and illusions that misled her and reinforced her convictions: the post hoc ergo propter hoc fallacy, confirmation bias, community reinforcement, the reverse halo effect, the illusion of understanding, and the illusion of control. He makes it very easy to understand why she thinks as she does. Hers was a very natural human response, but with education in critical thinking, we can hope to overcome those natural tendencies and avoid the kind of errors she made.

In a discussion of the ad hominem fallacy, he says something that I wish our critics would read and take to heart before assaulting us in our comments threads:

To refute my argument, you must show that my evidence is insufficient, that it is based on false or questionable assumptions, that the evidence I present is irrelevant, that I’ve omitted important evidence, or that I’ve given improper weight to various piece of evidence.

It’s not enough to accuse us of bias, financial gain, or pimping for Big Pharma; you have to address what we wrote rather than who we are, and show that what we have written is wrong (with credible references, please!).

His description of how his article on EMDR (eye movement desensitization and reprocessing) was attacked is typical of what we have repeatedly seen here on SBM. His critic:

asked if all his books were critical of something he knew nothing about

said EMDR had worked for her (anecdotal)

explained that there were exercises to do between sessions (which actually confirmed Carroll’s point that EMDR was essentially cognitive behavioral therapy)

complained that he should have taken EMDR training before he wrote

argued that he couldn’t possibly understand because he hadn’t experienced the agony of PTSD for himself

called him names

said his logic skills were atrocious and wondered how he ever got a professorship

said he doesn’t benefit anyone by saying EMDR doesn’t work (he didn’t claim that it doesn’t work, he claimed that it was a deceptive way of packaging cognitive behavioral therapy; she was attacking a straw man position that he did not hold)

He uses the NCCAM (National Center for Complementary and Alternative Medicine claim that 38% of Americans use alternative medicine to illustrate the ad populum fallacy. He illustrates other fallacies with examples from medicine. He discusses fears about cellphones and vaccines, testimonials, placebo effects, the appeal to tradition (“acupuncture is thousands of years old”), the appeal to authority (“Dr. Jay Gordon says vaccines aren’t safe.”) and how “authority” is not the same as expert scientific consensus.

He illustrates the availability heuristic with an experience Dr. Jerome Groopman had. He misdiagnosed a patient suffering from aspirin toxicity because her symptoms were compatible with the many cases of viral pneumonia he had recently been swamped with, so that the viral pneumonia diagnosis was readily available to his mind while aspirin toxicity was not.

In begging the question, the conclusion of the argument is entailed in its premises: abortion is murder, murder is illegal, so abortion should be illegal.

He covers a lot of recent psychological research into phenomena like change blindness, priming, the backfire effect, and many, many others.

He discusses the illusion of skill and the illusion of understanding (We can relate to that: we’ve seen many examples of the Dunning-Kruger effect among our commenters).

The clustering illusion: several cases of cancer in a neighborhood can occur by chance and don’t necessarily mean the inhabitants are being exposed to carcinogens in the soil or water. Communal reinforcement is when a claim becomes a strong belief through repeated assertion by members of a community. Confabulation: we all do it; our memories sometimes mix fact and fiction to recall things that never happened, and on a daily basis we invent reasons to explain how we feel.

Selection bias: Edzard Ernst tells how, as a young doctor, he gave mistletoe injections to cancer patients and was impressed by the results until he realized that his hospital was known throughout Germany for its approach, and desperate patients went there because they wanted that type of treatment and had high expectations.

Under causal fallacies (correlation is not causation) he covers the problem of multiple endpoints in small randomized controlled trials, where spurious correlations are expected due to the laws of chance. He also tells how doctors were interpreting signs of disc disease on MRI scans as an indication for back surgery until someone thought to do MRIs on patients without back pain and found that 2/3 of those showed the same changes.

I already knew the word pareidolia, but apophenia was new to me. It means the spontaneous perception of connections and meaningfulness of unrelated phenomena, the tendency to find personal information in noise, seeing patterns where there are none, the kind of subjective validation that cold reading exploits.

This is only a brief taste of the profusion of riches in this book. I highly recommend it to everyone. Whether you are a novice who needs a primer to learn about detecting logical fallacies or are already a seasoned pro, you are certain to learn something from The Critical Thinker’s Dictionary, and you are sure to enjoy the experience.

Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so), and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel. In 2008 she published her memoirs, Women Aren't Supposed to Fly.